1. Technical Field
The present invention relates to a fluid flow control valve, and particularly to a control valve for a vehicle hydraulic power steering gear.
2. Background Art
A fluid flow control valve includes first and second relatively movable valve members. A first valve member has a first fluid cavity, and a second valve member has a second fluid cavity. A land (projection) on one of the valve members has an outer surface extending between opposite edges. The land directs and controls fluid flow between the first and second fluid cavities upon relative movement of the valve members. The fluid flows across an edge of the land from one fluid cavity to another at relatively high velocity. Fluid tends to separate from the outer surface of the land and create turbulence during this high velocity flow. Noise often results because of this turbulence.
This problem occurs in a fluid flow control valve for a vehicle hydraulic power steering gear. A fluid flow control valve for a hydraulic power steering gear includes a valve sleeve and a valve core. The valve sleeve is tubular and has a plurality of longitudinally extending grooves (fluid cavities) in its inner surface. The valve core is coaxially disposed within the valve sleeve. The valve core has a cylindrical configuration with a plurality of axially extending grooves (fluid cavities) in its outer surface.
The valve sleeve and valve core are relatively rotatable to direct and control fluid flow between a pair of assist chambers of the hydraulic power steering gear. A respective land separates adjacent grooves (fluid cavities) in the valve core. A respective land also separates adjacent grooves (fluid cavities) in the valve sleeve. A land on the valve core is located centrally of a respective groove in the valve sleeve when the valve sleeve and valve core are in a neutral or centered position.
When the valve sleeve and valve core are in their neutral position, equal fluid communication is provided from an inlet passage, which communicates with a fluid pump, to (i) the assist chambers and (ii) reservoir. Upon relative rotation of the valve core and valve sleeve, one land moves to increase fluid communication between the inlet passage and one assist chamber and decrease communication of the assist chamber with the reservoir. Another land moves to decrease fluid communication between the inlet passage and the other assist chamber and increase communication of the other assist chamber with the reservoir. The fluid pressure in the inlet passage is relatively high. Thus, fluid flows at a high velocity across an edge of the other land from the inlet passage to the reservoir during relative rotation of the valve core and valve sleeve. This results in turbulence and undesirable noise.